A network monitoring device has hitherto existed, which guides, to the self-device, a packet coming from a pre-inspection terminal by sending as a response a MAC (Medial Access Control) address of the self-device if a sender terminal of a received ARP (Address Resolution Protocol) request packet is in a pre-inspection status (refer to Japanese Patent Laid-Open Publication No. 2008-271242).
Further, a countermeasure device has also existed, which restricts a communication service of a control target computer by changing a communication address, recorded in a first computer, of a second computer to a communication address of the countermeasure device and changing the communication address, recorded in the second computer, of the first computer to the communication address of the countermeasure device (refer to Japanese Patent Publication No. 4082613).